Apparatus for stepping up directcurrent voltage



July 26, 1949. c. c. SHUMARD APPARATUS FOR STEPPING UP DIRECT CURRENT VOLTAGE Filed March 50, 1948 TIME INVENTQR dfiarleJ C JZzzmard ATTORNEY Patented July 26, 1949 APPARATUS FOR STEPPING UP DIRECT- CURRENT VOLTAGE Charles C. Shumard, Moorestown, N. J., assignor to Radio Corporation oi America, a corporation of Delaware 1 Application March 30, 1948, Serial No. 17,959

(Cl. l7197) 8 Claims.

This invention relates to apparatus for obtaining a high D.-C. voltage from a lower voltage D.-C. source. More particularly, the invention relates to apparatus comprising a number of interconnected gas discharge tube circuits including capacitors for raising the level of D.-C. voltage output from a low voltage D.-C. source, which voltage increase is made at the expense of a lowering in output current.

Previous to the present invention, various types of circuits have been devised for stepping up D.-C. voltage. Some, such as shown in U. S. Patent 2,074,495, include circuits for both rectifying an A.-C. voltage and stepping up the value of the voltage above the original A.-C. level by utilizing the high voltage output efiect of the sudden collapse of flux in an inductance coil. Another type of circuit is shown in U. S. Patent 1,938,209. Here, the low voltage D.-C. current is first converted to A.-C., which is stepped up to higher voltage A.-C. and then rectified.

The present invention diifers from both of the above types of prior art devices. The voltage source used is a low voltage D.-C. source and the rise in voltage is obtained by converting the 11-0. voltage directly to a higher voltage A.-C. and then rectifying to D.-C. at the same high voltage level. In the present invention, the D.-C. voltage rise is due to successive increases in effective operating capacitor voltages obtained from alternately exciting series resonant circuits and, as an additional feature, to the unsym-' metrical use of the resonant circuits.

A principal object of the present invention is tov provide an improved apparatus for obtaining a high D.-C. voltage from a low voltage D.C. source.

Another object of the invention is to provide a transformerless means for stepping up D.-C. voltage, which is simple in structure and in operation.

Another object of the invention is to provide an apparatus for stepping up D.-C. voltage, which is easily adaptable to use with presently existing sources of low D.-C. voltage, and which is capable of raising the voltage to a level required by apparatus such as television kinescopes.

Still another object of the invention is to provide an improved apparatus for stepping up D.-C. voltage, which apparatus is easily adapted to cover a broad range'of operation by merely adjusting the circuit constants.

These and other objects will be more apparent and the invention will be more readily understood from the specification and the illustrative drawings, of which:

Fig. 1 is a schematic diagram of one embodiment of apparatus constructed in accordance with the present invention,

Fig. 2 is a schematic diagram of part of the circuit of Fig. l and has been included only for the purpose of aiding in the illustration of the derivation of suitable circuit constants for the circuit of Fig. 1,

Fig. 3a is a typical wave output of voltage that can be obtained from the circuit of Fig. 1 when symmetrical bias is used for the gas discharge tubes, and

Fig. 3b is a voltage wave output similar to Fill. 3a except that unsymmetrical bias is used.

Referring now to Fig. 1, it will be evident that the embodiment of the improved apparatus shown therein is comprised primarily of three circuit meshes. One of these, which may be termed mesh I, includes a low voltage supply Eb, an inductor L1, having an inherent series resistance R1 a thyratron tube V1, a capacitor C1 and the parallel combination of a capacitor C2 and resistor R0,. all in series. Another mesh, which may be termed mesh 2, comprises the capacitor C1, the parallel combination of a capacitor C3 and resistor R0,, an inductor L2 having an inherent series resistance R1. and a thyratron tube V2, all of which elements are inseries. The third mesh, which may be termed mesh 3, comprises a rectifier diode'tube V3 in series with the parallel combination of a capacitor C4 and resistor RC4, another parallel combination comprising the capacitor C: and resistor R0 and the capacitor C1.

The grid of tube V1 is provided with a grid leak resistor RG1, one end of which is connected between the Junction of the capacitor-resistor combination C3-Ro and the inductor L2. The grid of tube V2 is provided with a grid leak resistor RG2, one end of which is connected to ground.

It will be seen that the capacitor C1 is common I to all three meshes of the circuit and that the parallel capacitor-resistor combination C2-Ro is common to circuit meshes i and 3. The rectifier tube V; serves only to rectify A.-C. voltages appearing across that portion of the circuit to which it is connected.

The general principle of operation of the improved apparatus of the invention will first be explained by reference to the simplified diagram of Fig. 2. In this simplified diagram, the rectifier tube V; has been omitted. With the rectifier tube omitted, the circuit meshes reduce to mesh I and mesh 2, each of which includes a. gas discharge thyratron tube V; and V2. respectively. These thyratrons may be considered as single-pole, single-throw switches but allowing, however, conventional current to flow, when closed, only in one direction-that from anode to cathode, in each charge. Since the junction between the capacitors C1 and C2 is connected to the cathode of tube V2, the positive anode-to-cathode voltage of tube V: will be provided by the voltage to which capacitor C1 becomes charged and a negative grid-to-cathode voltage will be provided by the voltage to which capacitor C2 becomes charged. If,the values of the capacitors C1 and C: and of the resistor R are properly selected, the tube V: will not conduct when current flows in mesh i.

Current will continue to flow in mesh i only until capacitor C1 is fully charged, at which time the current would normally tend to reverse its direction but it cannot do so since the tube .71, is a unilateral conductor. The current, therefore, becomes zero and the voltage across the inductor L1 collapses leaving capacitor 01 fully charged to a voltage which depends upon. the circuit constants of circuit mesh I. This residual vole may be made by the proper choice of these stants to exceedthe plate supply voltage E sa that the cathode of tube V1 is left momentarily positive with respect to its anode. It will, therefore, start to deionize at this time.

The residual voltage constitutes the anodecathode voltage of tube V: but tube V2 will not begin to conduct until its grid bias voltage, which consists of the voltage across capacitor C2, has

decreased through the agency of the resistor R0 to a value insuflicient to maintain tube V: in a non-conducting state. When tube V: does suddenly begin conducting, capacitor C1 begins discharging through circuit mesh 2, charging capacitor C: and establishing a negative grid-tocathode voltage on tube V1 before the cathode of this tube becomes negative. with respect to its anode. Thus, if the bias on tube V: is maintained until tube V1 has deionized, tube V1 will not reconduct when tube V: becomes conducting.

Capacitor C1 will continue to discharge and charge to a voltage of opposite polarity but of lesser amplitude, the amplitude being less by the amount of the tube drop and dependent otherwise on the circuit constants of mesh 2. When this voltage is of maximum amplitude, the current would again normally reverse its direction. But since the thyratron V: is also a unilateral conductor, the current cannot reverse and so decreases to zero. The voltage across the inductor La collapses, leaving capacitor C1 charged to the above stated maximum value, the anode of tube V: being left negative with respect to its cathode.

- The tube V2 will, therefore, start to deionize.

The anode-to-cathode voltage now existing on tube V1 is the sum of two voltages, of which (1) is that provided by the low voltage supply Eb and (2) is the residual voltage on capacitor C1. The tube V1 will conduct again as soon as the negative grid-to-cathode voltage, provided by the voltage across the capacitor C3, is permitted to drop to a low enough value through the medium 3 or the leak resistor Re The capacitor C1 will then discharge from its previous stateof negative charge with respect to ground and charge to a positive value with respect to ground in a manner similar to that when the switch 8 was first closed, with the diflerence that its second maximum value will be substantially higher than its first maximum value. Also, the voltage across the capacitor C2 will now be greater, thus providing higher negative grid biasfor tube V2. Thus, it is noted that positive anode-tocathode voltages and the negative grid-to-cathode voltages will be proportionally higher. Similarly, higher voltages will be produced after the tube V: again conducts. From this, it can be seen that the voltages build up during the transient state to limiting values which are determined by the constants of the circuit meshes I and 2.

For proper operation of the above described circuit, suitable circuit constants must be chosen. Meshes 5 and 2 may have, but are not limited to, identical circuit parameters. In practical operation, the value of capacitor C1 is usually small compared to the values of capacitors C2 or C3 since it is desired to have the voltage across capacitor C1 quite large compared to the bias voltages appearing across capacitors C2 or C3. Moreover, it is desired to have the efiective series resistance small, which requires for a given time constant C2Rc that C2 be large and Re, small. For practical design, then, an efiective series resistance value is used in series with the capacitor to be also common to both meshes i and 2, which is the sum or all the efiective resistances around 35 mesh i and/or mesh 2; C2 or C3 is considered large compared to the value of C1, and L1 is generally made equal to La.

Having described the principles of operation of the simplified circuit of Fig. 2, the operation of the complete apparatus will now be described with reference toFlg. 1.

With the rectifier diode tube V: inserted, the circuit of mesh ,3 is completed. When, therefore, the capacitor C1 becomes positive with respect to ground, current may flow through the rectifier tube Va, charging capacitor C4. If reslstor R0 has a very high value, or is open, the maximum voltage appearing on the capacitor C4 will be substantially the maximum positive value which capacitor C1 attains (except for the drop in thetube Va). This voltage will be retained on the capacitor C4 when the polarity on capacitor C1 reverses, since tube Va is a unilateral conductor. The capacitor C4 would take no further charge after being charged initially, if load current were not being drawn through load resistor R0,. However, when load current is beingdrawn through resistor R0,, if the current drawn by it is not excessive, the capacitor C4 will be recharged ever time that capacitor C1 approaches and assumes its maximum positive value. The

load output is, therefore, seen to comprise the rectified output of the alternating voltage appearing across the capacitor C1.

Obviously, the current drawn by the load reslstor R0 must be less than the value which would be indicated by dividing the current supplied by the low voltage supply by the step-up voltage ratio, since there are some losses. The wave shape and hum content depend on the ratio of resistance R0 to the value of capacitor C4. For smaller load currents, the average D.-C. output voltage closely approaches the peak positive voltage appearing across capacitor C1. Con- 7 versely, the greater the load current the less the obtain a high negative D.-C. voltage.

voltage appearing across capacitor 01, since the efl'ective series resistance is ultimately greatly afl'ected and may finally result in an inoperative condition. For no load, the value of capacitor C4 will not aifect steady state operation.

The grid leak resistors RG1 and RG of. a few thousand ohms each, serve the double purpose of limiting grid current flow in the tubes V1 and V2, respectively, and regulating the time of discharge of capacitors C2 and C3, respectively.

Although the mode of operation of the apparatus has been described whereby there is obtained a stepped up positive D.-C. voltage, the apparatus may obviously be easily modified such that the voltage across capacitor C1 could be rectified to This is done by reversing the connections of the rectifier tube V3. The relative voltage output, however, would always be lower than in the case of a positive voltage.

The D.-C. positive voltage output of mesh 3 may be raised by the use of longer time constants for the combination capacitor-resistor Ca-Ro or shorter ones for the combination C2-Rc since this allows the charge on capacitor C1 to remain for a longer time after this capacitor has been charged to its maximum positive value. The process may be reversed, however, to equalize the forward and reverse voltages, if required.

Circuit values will now be given for apparatus capable of raising D.-C. voltages of about 30-60 to D.-C. voltages of about 100-300.

In all cases, in the following examples:

L1=L2=55 millihenries.

C1=0.25 f.; 04:0.05 t; Rc =1 megohm; RG1=RG2=5,000 ohms.

V1 and V2 may be type 884 thyratron tubes. Va may be a 5Y3GT, using plates in parallel.

Frequency of operation=84 cycles with 58 v. peak to peak ripple voltage. The voltage across capacitor C1 consisted of two equally spaced, approximately square wave-forms. The wave-form of the D.-C. output appeared as shown in Fig. 3a.

Example 2 For an unsymmetrical bias circuit in which C2=C3=25 t; Rc =68.8 ohms and Rc =330 ohms: I

Frequency of operation was '78 cycles. When Eb was 60 volts, the D.-C. output was 280 volts (an increase in voltage of 30 over the comparable voltage output of Example 1). At the same time, the ripple voltage decreased to 33 v., peak-topeak. This is due to holding the capacitor C1 at its positive value for a longer time by the longer time constant C3-Rc and the shorter time constant C2RC2. Capacitor C1 then aids in the filtering and raises the rectified voltage value. The wave-form of the rectified D.-C. voltage and the wave-shape of the voltage across capacitor C1 is shown in Fig. 3b.

It is obvious that in the above circuits higher values of D.-C. output voltage may be obtained when higher D.-C. supply voltages Eb are used. It is also apparent that considerably higher D.-C. output voltages may be obtained from voltages such as illustrated in the examples, by proper choice of circuit constants. A particularly useful form of the invention is one having circuit values which will permit the raising of a D.-C. supply of about 300 to that required for a klnescope. For this practical application, the circuits of the present invention offer improved means for obtaining a high D.-C. voltage at low current. Most power supplies of previous design have offered considerable power capacity but relatively low voltage output.

There has thus been described an improved apparatus for raising the voltage normally obtained from low level D.-C. sources to considerably higher values. The circuit components are few and may be arranged to form a compact unit. Although but a single embodiment of the invention has been shown in the drawings, it will be understood that various modifications may be made without departing from the spirit of the invention. For example, rectifying means, other than a diode tube, may be used and many different combinations of circuit constants may be selected. It is desired that the invention be limited only as indicated by the scope of the appended claims.

I claim as my invention:

1. Apparatus for deriving a raised D.-C. voltage from a low volt-age D.-C. source, said apparatus comprising a capacitor, means for alternately charging said capacitor in one direction from said source to a voltage level higher than that of said source and for discharging said capacitor and charging it in the opposite direction, and means for deriving a unidirectional voltage from the voltage appearing across said capacitor.

2. Apparatus for deriving a raised D.-C. voltage from a low voltage D.-C. source, said apparatus comprising a capacitor and means for applying the voltage from said source so as to charge said capacitor in one direction to a voltage level higher than that of said source, means for disconnecting said capacitor from said source and for discharging said capacitor and charging it in the opposite direction, and means for deriving a unidirectional voltage from the voltage appearing across said capacitor.

3. Apparatus for deriving a high D.-C. voltage from a low voltage D.-C. source having a certain voltage level, said apparatus comprising a first circuit mesh including a first gas discharge tube and a capacitor and means for applying the voltage from said source to charge said capacitor in one direction when current is flowing in said first tube, a second circuit mesh including said capacitor, a second gas discharge tube and means for preventing said first tube from conducting while said second tube is conducting, said second circuit mesh being connected so as to discharge said capacitor through said second circuit mesh during periods when said second tube is conducting whereby said capacitor becomes charged in the opposite direction, means for rendering said second tube conducting when said capacitor has become charged to a predetermined value in said one direction, means for rectifying the voltages appearing across said capacitor, and means for applying said rectified voltage to a load circuit.

4. Apparatus for deriving a raised D.-C. voltage output from a low voltage D.-C. source, said apparatus comprising a first circuit mesh including a gas discharge tube, a capacitor and means for applying the voltage from said source through said tube so as to charge said capacitor in one direction, a second circuit mesh including said capacitor, a second gas discharge tube and means for preventing said first tube conducting while said second tube is conducting, means in said first circuit mesh for preventing said second tube con ducting while said first tube is conducting, means for rendering said second tube conducting when said capacitor has become charged to a predetermined value in said one direction, means for dis charging said capacitor through said second circuit mesh during periods when said second tube is conducting, whereby said capacitor becomes charged in the opposite direction, and means for deriving a unidirectional voltage from the voltage appearing across said capacitor.

5. Apparatus according to claim .4 in -which said means for deriving a unidirectional voltage comprises rectifying means connected across said capacitor.

6. Apparatus for derivinga raised D. -C. voltage from a low voltage D.-C. source, said apparatus comprising a first circuit mesh including said source, a first gas dischargetube and a capacitor, said first discharge tube being connected so as to charge said capacitor in one direction when preventing the tube in the other circuit mesh from conducting during the'conductlng periods of its own tube, means for rendering each of said tubes alternately conducting at predetermined intervals, and means for deriving a unidirectional voltage from the voltage appearing across said capacitor.

aarsaancas crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,938,209- Biver et a1. Dec. 5, 1933 2,07%,495 Vance Mar. 3, 1937 

